1. Field of the Invention
The present invention relates to an image photographing apparatus including an image capturing device and a display device, a method of controlling the image photographing apparatus, and a control program.
2. Description of the Related Art
In Japanese Unexamined Patent Application Publication No. 2006-121344 (FIG. 1), there is disclosed a digital single-lens reflex camera which retreats a movable mirror from a photographing light-path, continuously captures subject images in a state where a focal plane shutter is opened, and displays the image on a monitor screen. In addition, in the digital single-lens camera described in Japanese Unexamined Patent Application Publication No. 2006-121344 (FIG. 1), when a photographer does not look into a finder eyepiece and manually operates a focus regulating operation member, the electronic viewfinder function is operated. Therefore, according to the digital single-lens reflex camera described in Japanese Unexamined Patent Application Publication No. 2006-121344 (FIG. 1), it is possible to easily perform the operation and to suppress an increase in power consumption.
Meanwhile, a digital camera, including a general backlight-fitted liquid crystal display device or a camera mounted on a cellular phone terminal, functions to capture image data output from an image capturing device, delivers the image data to a memory of a display device and makes it able to be displayed. That is, in the digital camera and the camera-equipped cellular phone terminal according to the related art, the display device is used as a so-called electronic viewfinder. Therefore, for example, even in a draft state when the photographing is actually not performed such as when a photographing angle is being determined, data reading/writing processes and image display processes are frequently executed. Therefore, in the digital camera and the cellular phone terminal, power consumption increases even in the draft state, so that the battery may be exhausted.
In addition, in the digital camera and the cellular phone terminal according to the related art, it takes a time to some degree from capturing by the image capturing device to updating the image data in the memory for the display device. For this reason, for example, when a moving photographic subject is photographed or when the photographer moves (that is, the camera moves), the image (image on the electronic viewfinder) on the screen of the display device is displayed with a delay compared with the real-world entity. In particular, when the photographing is performed under a low luminance environment, an exposure time of the photographing device is elongated and the output frame rate is slower. Therefore, the display image on the display device looks likes a moving image in which so-called frame omission occurs, and the movement of the subject image is often awkward and feels uncomfortable. In general, since the photographer determines timing for releasing the shutter while looking at the image on the display device, when the frame omission occurs in the display image as described above, it is difficult to release the shutter at a proper timing. As a result, a chance for a picture may be missed.
Further, the above problem hardly occurs in the film camera according to the related art in which the real-world entity can be directly confirmed via an optical finder, but becomes a special problem in the recent camera function of the digital camera or the cellular phone terminal. Of course, when the optical finder is provided at the digital camera or the cellular phone terminal so as to directly confirm the real-world entity by the photographer, the above-mentioned problem hardly occurs. However, in a case of the cellular phone terminal which is limited in housing volume capacity, it is not preferable to also provide the device such as the optical finder.
In addition, for example, when the capturing sensitivity of the image capturing device is increased or the light-gathering capability of the camera optical system is increased, a decrease in the above-mentioned output frame rate can be suppressed to some degree. However, when the highly-sensitive photographing device or the camera optical system with high light-gathering capability is provided, the cost is increased and the size is increased, which is not preferable. In addition, an uncomfortable feeling due to the display image on the display device may be reduced to some degree by using a CPU with image processing capability or by using a memory corresponding to a high-speed read/write operation. However, when the high-performance CPU or the memory corresponding to the high-speed read/write operation is mounted, the cost is increased and the power consumption is also increased.
Besides, a large number of digital cameras or a portion of camera-equipped cellular phone terminals are provided with a zoom function through which the photographing field angle is changeable, and the photographer performs the zoom operation while looking at the display image on the display device, so that the photographing is performed at a desired field angle. Then, the zoom operation is performed using a zoom-up/zoom-down button provided on the housing, or a zoom switch of a seesaw type. However, mounting locations of these buttons or the switches, operations of these buttons, the operation of the camera, and direction assignment of the zoom-up/zoom-down are different according to the types of cameras, so that it is difficult for these assignments to be distinguished to the photographer. For this reason, for example, the photographer may want to push the zoom-up button, but may mistakenly push the zoom-down button.